Four related patents which recite reliance on a patent application filed on Mar. 19, 1984 describe polymer dispersed liquid crystals. These are U.S. Pat. Nos. 4,671,618 to Wu et al, 4,673,255 to West et al, 4,685,771 to West et al, and 4,688,900 to Doane et al. These patents describe both a solvent method and a cure method for making PDLCs. In the solvent method, a fully polymerized polymer is dissolved in a solvent and the liquid crystal is distributed within the system. The solvent is driven off and the resulting solidified material is found to contain small droplets of liquid crystal distributed within it. In the cure method, the liquid crystal is dispersed in a medium of monomer and the monomer is subjected to polymerization conditions. Being inert with respect to the polymerization conditions and insoluble in the polymer, the liquid crystal becomes segregated into small domains scattered throughout the cured matrix. Segregation of the small droplets in either the cure method or the solvent method is known as phase separation.
Typical liquid crystal compositions include cyano biphenyls such as 4-cyano-4'-butylbiphenyl, 4-cyano-4'-hexylbiphenyl, 4-cyano-4'-heptylbiphenyl, 4-cyano-4'-octylbiphenyl, 4-cyano-4'-pentoxybiphenyl, 4-n-pentyl-n-cyano-biphenyl, and 4-cyano-4'-octoxybiphenyl. See West et al U.S. Pat. Nos. 4,685,771 and 4,673,255.
Fully polymerized polymethylmethacrylate ("PMMA") is used in solution in Examples II, V and VI of Wu et al U.S. Pat. No. 4,671,618. The PMMA, liquid crystal and solvent, such as acetone or trichloromethane, are mixed together to form a solution, and the solvent is driven off, causing the formation of a solid PMMA polymer with liquid crystal dispersed in it.
Murayama et al in U.S. Pat. No. 4,428,873 disclose the use of dissolved fully polymerized PMMA for the dispersion of other materials having electrooptical effects, such as p-nitroaniline, o-nitroaniline, 2-nitro-4-methoxyaniline, p-nitro-o-chloroaniline, 5-nitro-o-toluidine, 2-nitro-diphenylamine, 1,2-diamino-4-nitrobenzene, and p-nitrophenol.
Leslie et al in U.S. Pat. No. 4,869,847 use various monomeric media including several different acrylic monomers to polymerize to create very small liquid crystal domains. Difunctional acrylic oligomers are used by Gunjima et al in U.S. Pat. Nos. 4,818,070 and 4,834,509. Certain materials described as polyurethane prepolymers are employed by Benton et al in U.S. Pat. No. 3,872,050.
The reader may also be interested in "Polymer-Dispersed Liquid Crystals: Boojums at Work", MRS BULLETIN, January 1991, pages 22-28, Volume XVI, Number 1 (Materials Research Society) by J. William Doane, and "Polymer Dispersed Liquid Crystal Displays", by J. William Doane, Chapter 14, LIQUID CRYSTALS:APPLICATIONS AND USES, B. Bahadur, ed., World Scientific Publishing Co. (1990), on the use of liquid crystals for various practical purposes.